The problem of vehicles improperly crossing railroad tracks is becoming more pronounced due to a rise in both the average speed of trains and in the number of vehicles on the roads. Traditional systems for preventing vehicles from crossing the tracks at inopportune times have proved less than fully satisfactory, and traditional gates can be bypassed by impatient drivers who do not yet see a train coming, and, in any event, will not stop a vehicle that is out of control.
Energy absorbing system have been developed for preventing vehicles from crossing a railroad track by automatically deploying a restraining barrier across a roadway adjacent to a railroad track upon an approaching train. For example, U.S. Pat. No. 5,762,443 describes a heavy-duty shock absorber system with two pairs of concrete bunkers on either side of a railroad track, and a retractable capture net extending across the roadway between each pair of bunkers. In each bunker, the net is coupled to two hydraulic shock absorber mounted in a rotatable structure about a stachion, i.e., a large concrete filled steel pipe embedded 4 feet deep in a concrete foundation and extending 5 to 6 about ground level. The shock absorbers each have a piston and a cylinder, and operate by compression of fluid by the piston being driven into the cylinder in response to vehicle impact on the net.
U.S. Pat. No. 6,843,613 and U.S. Published Patent Application No. 2003/0016996, published Jan. 23, 2003, describe another heavy duty shock absorber system also utilizing pairs of bunkers on either side of a railroad track and stachions, but has the advantage of mounting each pair of hydraulic shock absorber using rotational flanges to the stachions, thereby avoiding the large rotatable structure of U.S. Pat. No. 5,762,443 for orienting the shock absorbers for operation by compression. In each bunker, the net is coupled to two hydraulic shock absorbers that are in turn attached to a flange rotatable about the bunker's stachion. Each of the hydraulic shock absorbers operates by extension of their piston from an initial compressed position away from the cylinder in response to vehicle impact on the net.
U.S. Patent Publication No. 2005/0117967, published Oct. 6, 2005, describes a heavy duty shock absorber system similar to U.S. Pat. No. 6,843,613, but without bunkers in which the two hydraulic shock absorbers also operate in extension in response to vehicle impact on the net. Unlike U.S. Pat. No. 6,843,613, the shock absorbers are oriented perpendicular, rather than parallel, to the railroad track when no vehicle is present. The net is supported on either side of a roadway by pivotal supports that are rotatable to an upright position when the net is needed.
One major drawback of the vehicle energy absorbing systems describes in the above-cited U.S. Patents and Published Applications is that they require a large amount of square footage for installation along roadsides due to the large size of the shock absorbers required to absorb the momentum generated by a vehicle impacting the net. For example, the shock absorbers used in U.S. Patent Publication No. 2005/0117967 and U.S. Pat. No. 6,843,613 are 5-6 feet when compressed when no impact is present, and can extend 8-11 feet in response to impact. Thus, it would be desirable to reduce the size of shock absorbers used in these systems, while still providing the necessary energy absorption of an impacting vehicle. Such reduction in the overall size of the vehicle energy absorbing system can enable their installation along more railroad crossings where space about the roadside is limited. It would further be desirable if the stachions required in the above cited U.S. Patents and Published Applications were no longer required, thereby making installation easier and less costly.